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A317394 Positive integers that have exactly four representations of the form 1 + p1 * (1 + p2* ... * (1 + p_j)...), where [p1, ..., p_j] is a (possibly empty) list of distinct primes. 2
211, 261, 421, 426, 441, 484, 535, 540, 591, 621, 634, 667, 683, 691, 715, 726, 732, 761, 771, 776, 778, 794, 818, 853, 862, 871, 925, 970, 979, 987, 989, 1011, 1021, 1023, 1038, 1074, 1086, 1105, 1114, 1141, 1171, 1176, 1184, 1190, 1197, 1222, 1261, 1266 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..20000

FORMULA

A317241(a(n)) = 4.

MAPLE

b:= proc(n, s) option remember; local p, r; if n=1 then 1 else r:=0;

      for p in numtheory[factorset](n-1) minus s while r<5

        do r:= r+b((n-1)/p, s union {p}) od; `if`(r<5, r, 5)

      fi

    end:

a:= proc(n) option remember; local k; for k from

     `if`(n=1, 1, 1+a(n-1)) while b(k, {})<>4 do od; k

    end:

seq(a(n), n=1..100);

CROSSREFS

Column k=4 of A317390.

Cf. A317241.

Sequence in context: A246136 A087833 A240918 * A096706 A001583 A308790

Adjacent sequences:  A317391 A317392 A317393 * A317395 A317396 A317397

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jul 27 2018

STATUS

approved

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Last modified April 4 04:53 EDT 2020. Contains 333212 sequences. (Running on oeis4.)